Interpretive Summary: The United States Department of Agriculture (USDA) developed inbred lines of Hereford cattle to facilitate use of heterosis by beef producers. Line 1 is the only surviving line from 56 lines that were originally developed and has seen considerable application in the purebred industry. The objective of this research was to determine the impact of Line 1 on the South African Hereford population. Genetic relationships were calculated using both pedigree and genomic data. Based on pedigree information, the relationship of the South African Hereford population to Line 1 was 24%, approximately equivalent to each South African Hereford having one grandparent from Line 1. Using genomic data, the probability that South African Hereford cattle belonged to the Line 1 population was estimated to be 38%. This research documents one aspect of the global impact of the Line 1 Hereford, a product of long term research conducted by USDA Agricultural research Service and predecessor agencies.

Technical Abstract:
The goal of this research was to document the influence of Line 1 Hereford cattle, developed by the United States Department of Agriculture (USDA) at its research facility in Miles City, Montana, on Hereford cattle in South Africa. Analytical approaches made use of both recorded pedigree and microsatellite marker information. Cattle with recorded performance data in South Africa were mated with Line 1 Hereford sires in silico and inbreeding coefficients were calculated for the resulting progeny. The relationship between South African and Line 1 Hereford cattle populations was twice the maximum inbreeding coefficient for the progeny of each South African animal. Thus, calculated pedigree relationship of Hereford cattle registered in South Africa with Line 1 was 24%. Thirty-six South African Hereford cattle along with a sample of 64 Line 1 animals were genotyped with 34 microsatellite markers. Based on a Bayesian model-based clustering method, the probability that the South African Hereford cattle were members of Line 1 was 0.38 ± 0.08. This research documents one aspect of the far reaching effects of the Line 1 Hereford population.